Fortigate-exporter-discovery

What's Changed
* feat: support to act as an exporter for fortimanager related metrics. by thenodon in https://github.com/thenodon/fortigate-exporter-discovery/pull/3


**Full Changelog**: https://github.com/thenodon/fortigate-exporter-discovery/compare/v0.3.3...v0.4.0

What's Changed
* Add http service discovery mode
* Add basic auth
* Add a simple cache for the fetched data from Fortimanager

**Full Changelog**: https://github.com/thenodon/fortigate-exporter-discovery/compare/v0.1.2...v0.3.0